Mammary cancer is the leading cause of death among women. About 5-10% is the familial cases, which are attributed to deleterious mutations in BRCA1 and BRCA2. The majority of the remaining breast cancer cases are also suspected to contain genetic component that affects BRCA1/BRCA2. Preliminary studies revealed that quinone oxidoreductases (NQO1 and NQO2) might protect against mammary toxicity, carcinogenicity and metastasis. Disruption of NQO1 gene in mice led to mammary gland intraductal hyperplasia and DMBA-induced mammary tumors that metastasized to lung, liver and spleen. NQO2 is highly homologous to NQO1 and is also expected to protect against mammary cancer. Preliminary studies also showed that chemical/radiation stress responsive NQO1 and NQO2 regulate stability of BRCA1 against 20S proteasomal degradation that contributes to protection against DMBA-induced mammary cancer. In addition, NQO1 and NQO2 control stability of C/EBPa that suppresses matrix metalloproteinase9 (MMP9) and protect against metastasis. The overall goal of the current studies is to investigate the hypothesis that NQO1 and NQO2 are endogenous factors in protection against mammary toxicity, carcinogenicity and metastasis. Three aims are planned. Aim 1 will test the hypothesis that NQO1 and NQO2 are biomarkers of susceptibility to DMBA-induced and spontaneous mammary cancer and metastasis. In addition, this aim will also investigate the hypothesis that NQO1 and NQO2 metabolic detoxification of catechol quinones and/or control of factors in DNA repair, growth/differentiation and apoptosis protect against mammary cancer. Wild type, NQO1-/-, NQO1+/- and NQO2-/- mice exposed to DMBA will be analyzed for mammary tumor frequency/multiplicity and metastasis. NQO1-/- and NQO2-/- mice will also be crossed with MMTV-Neu-p53 mice and assessed for increase in frequency and multiplicity and decrease in time of spontaneous mammary tumor development and metastasis. In addition, mice exposed to DMBA or estradiol will be analyzed for metabolic activation/detoxification of catechol estrogen quinones and key molecular changes in NQO1-/- and NQO2-/- mice leading to increased susceptibility to DMBA-induced mammary cancer/metastasis, as compared with wild type mice. Aim 2 will determine mechanism of NQO1 and NQO2 control of stability of BRCA1 against 20S proteasomal degradation leading to protection against mammary cancer. Western, immunoprecipitation, transfection, protein degradation, domains interaction, and phosphorylation assays will study NQO1/NQO2 control of BRCA1/BRCA2 stability against 20S degradation. Stress induced gain/loss, of NQO1/NQO2 and 20S proteasome interactions with BRCA1/BRCA2 will be followed. Aim 3 will elucidate the mechanism of NQO1 and NQO2 control of MMP9 protein leading to protection against mammary cancer metastasis. We will test the hypothesis that NQO1 and NQO2 stabilization of C/EBPa against 20S proteasomal degradation leads to suppression of MMP9 with implications in protection against metastasis. Studies are significant since human individuals carry deleterious mutations in NQO1 and NQO2 and are deficient in these proteins.